Lower Crust from Beneath the Arctic Ice

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Abstract

Three major layers compose the oceanic crust: sediment, basalt, and gabbro, a total thickness normally between 5-10 km. The deepest, least accessible, and least understood of these is gabbro, an crystalline magmatic rock composed of the main minerals pyroxene, calcium plagioclase, and olivine. We studied rocks from the gabbro layer from Gakkel Ridge, Arctic Ocean, which is the thinnest crust of the major oceans. This ocean has the slowest seafloor spreading of any mid-ocean ridge. Such ultra-slow spreading rates (<20mm/year) are accompanied by a decreased volcanic melt production in the mantle beneath the ridge. The composition of gabbro from Gakkel Ridge is affected by processes such as low pressure melt impregnation in the mantle and low degrees of mantle melting. My hypothesis is that the composition of gabbro in the Arctic ocean will be different than the composition in the Pacific ocean, fast spreading mid ocean ridge. This project was completed with contributions from Gelu Costin from the Department of Earth and Atmospheric Science, Rice University.